The police watchdog has demanded greater scrutiny of Tasers and warned the weapons are being used disproportionately against black men and mentally ill suspects.
The Independent Office for Police Conduct (IOPC) said transparency was needed following a government push to arm up to 10,000 more police officers with stun guns.
Last month, a coroner warned that “future deaths will occur unless action is taken” on Taser use after examining the death of 30-year-old father Marc Cole.
“The IOPC recognises that the use of Taser is important in helping officers respond to often dangerous and challenging situations,” said director-general Michael Lockwood.
“However, more officers are now carrying Taser and there are growing concerns both locally and nationally about its disproportionate use against black men and those with mental health issues.”
Taser incidents in England and Wales rose by 30 per cent to 22,000 in England and Wales in 2018-19 and the year saw a record of 2,500 discharges.
One in five incidents involved black people, who make up only 3.3 per cent of the population, although Tasers were only fired 10 per cent of the time - as opposed to merely drawn or aimed.
Mixed-race suspects were most likely to be involved, at 13 per cent of incidents, followed by white people on 12 per cent, and police must record their use of the weapons any time they are drawn.
The IOPC said it was currently investigating four recent incidents, including one that sparked protests in Manchester on Saturday.
Footage showed a black man, who was later charged with a series of criminal offences including drink-driving, being Tasered while his young son screamed “daddy”.
Days before, a man was left with life-changing injuries in London after being Tasered as he jumped over a wall while running from police. Three officers are under investigation by the IOPC.
The watchdog is also investigating an incident in London on 6 May, when a Taser was aimed at a man who had been stopped for a drugs search.
A fourth Taser incident involving West Midlands Police is being examined.
“I want to reassure those communities that we take these matters very seriously and will be thorough and impartial in looking at what happened,” Mr Lockwood said.
“We need transparency around how and when Tasers are used, and a visible demonstration that police forces are learning from their experiences,” he added, calling for “robust oversight” to build confidence in the way police officers use force.
Mr Lockwood said he was concerned that the spate of incidents had damaged community relations and public confidence in police.
“There must be more research to understand issues of disproportionality as well as assurance and scrutiny of Taser use at a local level … not just when something goes wrong, but 365 days a year,” he added.
“These incidents have only come to our attention because of the level of injury sustained or via social media. Given the number of times Tasers are deployed, there may be other incidents which are not being scrutinised.”
The IOPC said it would discuss the issue with police forces, police and crime commissioners, community groups and campaigners over the coming weeks.
The government announced last September that up to 10,000 extra police officers were to be armed with Tasers, with £10m being made available to increase the number of trained and equipped officers.
At the time, ministers were accused of risking an “escalation of violence” by funding more stun guns for bobbies on the beat, with human rights campaigners slamming the announcement as a “knee-jerk” reaction to rising attacks on officers, and warning that it could put public safety at risk.
Only £6.7m of the funding has so far been taken up, to purchase around 8,200 new Tasers for 41 of the 43 forces in England and Wales.
Tasers were originally introduced as a “less lethal weapon” for firearms officers in 2003, but the remit has gradually been widened.
The Police Federation, which represents rank-and-file officers, called them an “essential piece of equipment which have saved many police officers from serious injury or worse”.
But support for the weapons among chief constables varies, with some fearing that their increased use damages public relations and undermines the unarmed nature of British policing.
The National Police Chiefs’ Council (NPCC) has not completed research on how best to protect officers and previously said Tasers were “not the answer to all violent or threatening situations”.
Martyn Underhill, of the Association of Police and Crime Commissioners, said he had asked for an urgent review of Taser training and would meet with the IOPC.
He added: “It is clear there are concerns at the use police use of Taser in contentious circumstances, including in relation to levels of disproportionality with BAME communities.”
A Home Office spokesperson said: “Our police officers put themselves in harm’s way to protect us and Taser is an important tactical option in dangerous situations to keep themselves and the public safe.
“However, any use of force by the police must be lawful, proportionate and necessary, and subject to proper scrutiny.”